The present invention relates to a semiconductor device having a nitride film for preventing external hydrogen from entering the device and, more particularly, to a semiconductor device having a gate oxide film with an improved breakdown life.
Generally, a semiconductor device has a nitride film on the substrate surface to prevent external hydrogen from entering the device. FIG. 3 shows a conventional semiconductor device having a nitride film 8 on a gate electrode. Referring to FIG. 3, a source region 4 and a drain region 5 are formed on the major surface of a semiconductor substrate 1, i.e., an Si substrate to be separated from each other. A gate insulating film 2 consisting of a silicon oxide film is formed on the semiconductor substrate 1 between the source region 4 and the drain region 5. A gate electrode 3 is formed on the gate insulating film 2.
Side wall films 6 are formed on both sides of the gate insulating film 2 and the gate electrode 3 so that the diffusion layer in the semiconductor substrate 1 has an LDD (Lightly Doped Drain) structure. The gate electrode 3 and the side wall films 6 are covered with a thin oxide film 12. The entire surface of the semiconductor substrate 1 including the oxide film 12 is covered with the nitride film 8. An insulating interlayer 13 is formed on the nitride film 8, and a plasma nitride film 14 is formed on the insulating interlayer 13.
As described above, conventionally, by forming the nitride film 8 immediately above the gate electrode 3, external hydrogen is prevented from entering the device, and degradation in hot-carrier resistance is suppressed.
However, formation of the nitride film 8 immediately above the gate electrode 3 poses various problems. The stress of the nitride film 8 largely changes due to thermal hysteresis in the process of forming the insulating interlayer 13 or plasma nitride film 14 on the nitride film 8. Consequently, this stress acts on the gate insulating film 2 to decrease the reliability life of the gate insulating film 2.